My girlfriend has a 99 vulcan. When the engine is at normal operating temperature and the heat is on, the air is lukewarm. When I bring the RPMs up, the heat then blows hotter air. The higher the fan speed, the higher I have to bring the RPMs up the get the heat to actually blow hot air. The temp gauge looks like it is functioning properly and doesn't drop when the car is moving. I'm thinking that the cooling system needs to be flushed but I'm open to other ideas.